This invention relates to pressure-sensitive adhesive coated, tamper-indicating articles.
A variety of pressure-sensitive adhesive coated articles, e.g., labels and stickers, have been developed to provide visual evidence of tampering. Generally, the articles have been designed to leave a tenaciously-adhered, residual indication of tampering on substrate surfaces. Such articles and/or their residues can be removed only with the aid of solvents and/or mechanical scraping, which can damage substrate surfaces.
Thus, for valuable substrates (i.e., non-disposable, reusable substrates such as automobile windshields), there is a need in the art for an article that displays permanent evidence of tampering when any attempt is made to remove it from the substrate, but that either does not leave any residue upon removal or provides a residue that is removable without the aid of solvents or mechanical scraping. Such an article should exhibit sufficiently high adhesion to the substrate to enable it to remain adhered during normal use conditions and should provide sufficient indication of tampering to render it non-transferable (e.g., to another vehicle).
Briefly, in one aspect, this invention provides a tamper-indicating article for use on valuable, i.e., non-disposable or reusable, substrates. The article comprises (a) a pressure-sensitive adhesive film or pressure-sensitive adhesive-coated tape that can be removed, without exhibiting cohesive failure, from a substrate surface (e.g., an automobile windshield) by stretching the film or tape; and (b) at least one damageable layer that shows cohesive or intralayer failure when an attempt is made to remove the article from the substrate surface. Preferably, component (b) comprises indicia and/or a holographic layer, and component (a) comprises a pressure-sensitive adhesive film or pressure-sensitive adhesive-coated tape that can be removed by stretching at an angle of about 45 degrees to the substrate surface. The article also preferably further comprises a retroreflective layer.
The tamper-indicating features of the article of the invention derive from the incorporation of a damageable layer, e.g., a layer that is destructible (in whole or in part) or that is irreversibly deformable. The cohesive strength of this layer (component (b)) is less than the adhesive strength between component (a) and the substrate, and this adhesive strength is less than the cohesive strength of component (a). The article thus remains durably bonded to a substrate surface under normal use conditions. However, an attempt to forcibly remove the article from the substrate results in the cohesive or intralayer failure of component (b), accompanied by the separation of components (a) and (b). Component (a) remains substantially intact and bonded to the substrate surface. The article thereby provides sufficient indication of tampering to render it non-transferable to another substrate.
Although the tamper-indicating article of the invention can be used on a wide variety of substrates, it is especially useful for application to substrates that are not single-use, disposable substrates but rather that are valuable substrates for which continuous or repeated use is desired. An attempt to remove the article from a substrate will activate its tamper-indicating features, yet the portion of the article remaining on the substrate (after activation) can be easily and completely removed without the need for chemical agents (e.g., organic solvents) or mechanical tools (e.g., knives or scrapers). The prior art problem of substrate damage is thereby avoided. Thus, the article is particularly useful as a security label for a vehicle window, bumper, or license plate; as a closure seal for brief cases, computer disc drives, doors, and filing cabinets; and as a security label for identification cards and other documents.
In another aspect, this invention also provides a substrate bearing the tamper-indicating article of the invention.